#include<stdio.h>
#include<stdlib.h>

#define PI 3.14159

int main() {
    // 设置控制台代码页为 65001 (UTF-8)，防止乱码
    system("chcp 65001 > nul");
    printf("请输入圆的半径：");
    double radius, real_area;
    scanf("%lf", &radius);
    if (radius <= 0) {
        printf("半径必须大于0！\n");
        return 1;
    }
    real_area = PI * radius * radius;
    printf("半径为%.2f的圆的面积为：%.2f\n", radius, real_area);

    return 0;
}